Having grown to an enormous state scattered over most of the German Empire, Prussia found it convenient to organize administrative subdivisions called provinces. Each of these had "land colors" or Landesfarben.

Provinz Hannover

The colours of the [Prussian] province adopted in 1887 were the same as the ones of the former kingdom: yellow over white. This flag can still be seen today, but is rarely used.

Pascal Vagnat, 9 September 1996

Yellow-white bicolor. Adopted 22 October 1892. In use for local and regional authorities since 1952.

Norman Martin, 1998

The coat of arms of the Prussian province and later Land of Hanover was Gules a horse Argent. It can still be used.

Pascal Vagnat (?)

[According to the website of the Hanoverian monarchists] after the Prussian annexation, in 1873, a provincial flag was designed with the lion of Lüneburg instead of the horse, but this was so unpopular, that finally in 1881 the horse was readopted (without the green field).

Großherzogtum Posen, Provinz Posen

by Santiago Dotor

Red-white horizontal bicolor. In use 1815 to 1886.

Norman Martin, 20 January 1998

Grand Duchy of Poznan (semi-autonomous part of Prussia) had a flag horizontally red-white. In 1849 the Grand Duchy was renamed to Province of Poznan (German Provinz Posen) and the autonomy was suppressed.

In 1886 the flag was changed by the Prussian authorities into horizontal white-black-white triband, because the former was far too similar to Polish. White-black-white triband was the official provincial flag till 1918.